Method of di/dt current sensing

ABSTRACT

An integrated circuit package includes a power circuit having a plurality of transistors which form part of a main current loop of the power circuit, the plurality of transistors arranged in one or more layers of the integrated circuit package. The integrated circuit package further includes a conductive loop electrically decoupled from the plurality of transistors. The conductive loop is spaced apart from the plurality of transistors and in close enough proximity to at least part of the main current loop so that the conductive loop is operable to generate a voltage proportional to an electromagnetic field generated responsive to a change in current in the main current loop. A method of fabricating the integrated circuit package is also provided.

PRIORITY CLAIM

This application is a Divisional of U.S. patent application Ser. No.12/887,835, filed Sep. 22, 2010, said application incorporated herein byreference in its entirety.

BACKGROUND

Current sensing is required for many types of circuit operationsincluding current mode control, current monitoring, over-currentprotection and current dependent operation modes. Sensing current in acircuit typically involves the use of resistive elements. Senseresistors increase resistance and lower efficiency. An inductor can beused to sense the current instead of a sense resistor. In yet anotheralternative, the drain-to-source on resistance of a MOSFET(metal-oxide-semiconductor field effect transistor) can be measured todetermine the amount of current flowing in the circuit.

Each of these conventional current sensing techniques require thecurrent sensing signal generated by the sensing element to be routedback to a controller which manages one or more current related functionsof the circuit. For example, when implementing current dependentoperations in a driver stage of a power circuit, some means must beprovided for sensing the current and communicating information about thesensed current back to the circuit. With discrete circuits, thistypically involves providing additional feedback traces for connectingthe sense device to the circuit and for feeding back the sensed currentlevels to the controller. All of these additional feedback traces mustbe carefully routed e.g. on a printed circuit board or within amulti-layer package to ensure normal circuit operation is not adverselyaffected by the current feedback mechanism, thus complicating the designof the board or package. Also, sensed current signals are usually verysmall in magnitude and can be rendered unreliable under certain noiseconditions.

SUMMARY

According to an embodiment of a circuit, the circuit comprises a powercircuit and a current sensing circuit. The power circuit has a maincurrent loop. The current sensing circuit is spaced apart from andelectrically decoupled from the power circuit. The current sensingcircuit is operable to generate a voltage proportional to anelectromagnetic field generated responsive to a current change in themain current loop of the power circuit and generate a currentinformation signal based on the voltage. The current information signaldescribes the current in the main current loop.

According to a method of operating the circuit, the method comprisesgenerating an electromagnetic field by the power circuit responsive to acurrent change in the main current loop of the power circuit andgenerating a voltage by the current sensing circuit that is proportionalto the electromagnetic field. The method further includes generating acurrent information signal by the current sensing circuit based on thevoltage, the current information signal describing the current in themain current loop.

According to an embodiment of an integrated circuit package, the packagecomprises a power circuit and a conductive loop. The power circuitincludes a plurality of transistors which form part of a main currentloop of the power circuit. The plurality of transistors is arranged inone or more layers of the integrated circuit package. The conductiveloop is electrically decoupled from the plurality of transistors. Theconductive loop is spaced apart from the plurality of transistors and inclose enough proximity to at least part of the main current loop so thatthe conductive loop is operable to generate a voltage proportional to anelectromagnetic field generated responsive to a change in current in themain current loop. A first external terminal can be coupled to one endof the conductive loop and a second external terminal can be coupled tothe other end of the conductive loop for providing connection points forthe conductive loop at an external surface of the integrated circuitpackage.

According to a method of fabricating the integrated circuit package, themethod comprises arranging the power circuit including the plurality oftransistors which form part of the main current loop of the powercircuit in one or more layers of the integrated circuit package andarranging the conductive loop so that the loop is electrically decoupledfrom and spaced apart from the plurality of transistors. The conductiveloop is arranged in close enough proximity to at least part of the maincurrent loop so that the conductive loop is operable to generate avoltage proportional to an electromagnetic field generated responsive toa change in current in the main current loop.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the figures are not necessarily to scale, insteademphasis being placed upon illustrating the principles of the invention.Moreover, in the figures, like reference numerals designatecorresponding parts. In the drawings:

FIG. 1 illustrates an embodiment of a circuit including a power circuitand a current sensing circuit electromagnetically coupled to the powercircuit.

FIG. 2 illustrates an embodiment of the current sensing circuit shown inFIG. 1.

FIG. 3 illustrates another embodiment of the current sensing circuitshown in FIG. 1 and a waveform diagram associated with the operation ofthe current sensing circuit.

FIG. 4 illustrates a top-down plan view of an embodiment of a conductiveloop of the current sensing circuit spaced apart from and positionedover at least a portion of the power circuit.

FIG. 5 illustrates a schematic view of an embodiment of an integratedcircuit package including a power circuit and a current sensing circuitelectromagnetically coupled to the power circuit.

FIG. 6 illustrates a schematic view of another embodiment of anintegrated circuit package including a power circuit and a currentsensing circuit electromagnetically coupled to the power circuit.

DETAILED DESCRIPTION

FIG. 1 illustrates an embodiment of a circuit 100 that includes a powercircuit 110 and a current sensing circuit 120 electromagneticallycoupled to the power circuit 110. The power circuit 110 and currentsensing circuit 120 can be integrated on the same or differentsemiconductor die. Alternatively the current sensing circuit 120 can bepart of the package assembly housing the power circuit 110. The powercircuit 110 has a main current loop. In some embodiments, a driver 112is included in the same package as the main current loop of the powercircuit 110. The power circuit 110 operates at a high enough power levelso that an electromagnetic field, indicated by the curved lines in FIG.1, is generated responsive to a phase transition in the main currentloop and is strong enough to be sensed by the current sensing circuit120. The current sensing circuit 120 includes a conductive loop 122positioned within the electromagnetic field generated by the powercircuit 110. The conductive loop 122 can be integrated in the samesemiconductor die as the power circuit 110, or included within orattached to a package housing the power circuit 110.

A voltage ν_(antenna) develops across the terminals of the conductiveloop 122 that is proportional to the electromagnetic field generated bythe power circuit 110. The conductive loop 122 in effect functions as anantenna. The voltage produced by the conductive loop 122 corresponds tothe current in the main current loop of the power circuit 110 and issensed by a sense circuit 124 included in or associated with the currentsensing circuit 120. The voltage of the conductive loop 122 can berectified, amplified, smoothed, etc. by the sense circuit 124 to providea signal v_(sense) that can be processed by an analysis circuit 126included in or associated with the current sensing circuit 120.

The analysis circuit 126 generates a current information signalcurrent_info based on the output of the sense circuit 124. The currentinformation signal describes the current in the main current loop and isprovided to a controller 130. The controller 130 manages one or morecurrent dependent operations of the power circuit 110 in response to thecurrent information signal such as operation of the driver 112. Forexample, the controller 130 can implement current mode control, currentmonitoring, over-current protection and/or one or more current dependentoperation modes at the power circuit 110. The analysis circuit 126 maybe included in or associated with the controller 130 instead of thecurrent sensing circuit 120 in some embodiments. According to theseembodiments, the output of the sense circuit 124 is provided to thecontroller 130 which analyses and processes the received signal andtakes corresponding action.

In either case, the controller 130 implements one or more currentrelated functions without the current sensing circuit 120 beingelectrically coupled to the power circuit 110. That is, the currentsensing circuit 120 is spaced apart from and electrically decoupled fromthe power circuit 110. During operation of the circuit 100, anelectromagnetic field is generated by the power circuit 110 responsiveto a current change in the main current loop of the power circuit 110. Avoltage proportional to the electromagnetic field develops across theterminals of the conductive loop 122 included in or associated with thecurrent sensing circuit 120. The sense circuit 124 senses the voltageand the analysis circuit 126 generates the current information signalbased on the sensed voltage and provides the current information signalto the controller 130 for implementing one or more current dependentoperations at the power circuit 110 based on the current informationsignal.

FIG. 2 illustrates an embodiment of the sense circuit 124 included in orassociated with the current sensing circuit 120. The sense circuit 124includes a plurality of diodes D1, D2, D3, D4 coupled together to form abridge rectifier 200. The bridge rectifier 200 is coupled to theterminals of the conductive loop 122 and rectifies the voltageelectromagnetically induced at the conductive loop 122. The sensecircuit 124 also includes a capacitor 210 coupled to the rectifier 200.The capacitor 210 accumulates charge responsive to the rectifier output.The voltage across the capacitor 210 is related to the current in themain current loop due to the electromagnetic coupling between theconductive loop 122 of the current sensing circuit 120 and the powercircuit 110. The sense circuit 124 further includes a switch device 220coupled to the capacitor 210. The switch device 220 periodically resetsthe capacitor 210 responsive to a reset signal e.g. by discharging thecapacitor 210 to ground. In some embodiments, the switch device 220 isactuated so that the capacitor 210 integrates the rectified voltage overa plurality of sampling periods prior to resetting the capacitor 210 sothat the sensed voltage is smoothed or averaged over some period oftime.

The magnitude of the voltage induced in the conductive loop 122 of thecurrent sensing circuit 120 is influenced by several factors. Forexample, the transconductance i.e. the ratio of current change at thepower circuit 110 to the voltage change at the conductive loop 122 is afunction of the current as given by:

g _(fs) =f(I _(D))  (1)

The transconductance is monotone rising and therefore di/dt increasesfor higher output current levels at the power circuit 110 unless thephase transition at the main current loop is inductively limited by theconductive loop 122. In addition, reverse recovery current alsoincreases with output current. The voltage induced in the conductiveloop 122 is a function of both of these effects.

The analysis circuit 126 senses the capacitor voltage V_(c) andinterprets the sensed voltage to generate the current information signalused by the controller 130. In one embodiment, the analysis circuit 126defines one or more threshold values related to a given sensed voltagesignature. The analysis circuit 126 translates the sensed capacitorvoltage into a current value for the power circuit 110 based on thethreshold values. In one embodiment, the analysis circuit 126 comparesthe sensed capacitor voltage to the thresholds and generates the currentinformation signal based on which of the thresholds the sensed voltageexceeds. The analysis circuit 126 can analyze the sensed capacitorvoltage over several sampling periods so that the current informationsignal provided to the controller 130 is smoothed or averaged over someperiod of time. The analysis circuit 126 can be an analog-to-digitalconverter, amplifier, trigger circuit or any other circuit suitable forsensing and interpreting the voltage of the sense circuit capacitor 210.The analysis circuit 126 is not shown in FIG. 2 for ease of illustrationonly.

FIG. 3 illustrates another embodiment of the sense circuit 124 includedin or associated with the current sensing circuit 120. As with FIG. 2,the analysis circuit 126 is not shown in FIG. 3 for ease of illustrationonly. According to the embodiment shown in FIG. 3, the diodes D1, D2,D3, D4 that form the bridge rectifier 200 are silicon rectifier diodeseach of which has a negative forward voltage temperature coefficient. Assuch, higher temperatures result in a lower forward voltage drop acrossthe diodes D1, D2, D3, D4. The switch device 220 is implemented as aMOSFET Q1. The transconductance of the MOSFET Q1 decreases astemperature increases. Therefore the communicated signal voltagedecreases as the temperature of the sense circuit 124 increases. Thecircuit 100 can be tuned so that the decreased communicated voltage bythe MOSFET Q1 is offset by the lower voltage drop of the bridgerectifier 200. For example, tuning can be performed based on thecoupling between the current sensing circuit 120 and the power circuit110. A relatively weak coupling between the power circuit 110 and theconductive loop 122 gives the diodes D1, D2, D3, D3 more weight. Assuch, a higher current limit occurs at lower temperatures and a lowercurrent limit occurs at higher temperatures.

FIG. 3 also illustrates a waveform diagram for the capacitor voltageV_(c) sensed by the sense circuit 124 during different periods ofoperation. The analysis circuit 126 periodically resets the capacitor210 after every one or more switching cycles by activating the resetsignal applied to the gate of the MOSFET Q1. The capacitor 210integrates the rectifier output over a plurality of sampling periodsprior to being reset when the reset signal applied to the gate of theMOSFET Q1 is activated once every plurality of sampling periods.Alternatively, the capacitor 210 can be reset every sampling period bycorrespondingly activating the reset signal. In either case, the chargeaccumulated by the capacitor 210 depends on the energy harvested duringa phase transition at the main current loop of the power circuit 110.The charge accumulated by the capacitor 210 is proportional to thecoupling factor k of the conductive loop 122 and yields a voltage acrossthe capacitor 210 as given by:

ν_(antenna) =k·L·di/dt  (2)

where L is the inductance of the conductive loop 122 and di/dt is therate of current change in the main loop of the power circuit 110.

If the inductance of the conductive loop 122 limits the phase transitionin the main current loop of the power circuit 110 as describedpreviously herein, di/dt is fixed and the voltage induced at theconductive loop 122 is attenuated. In another scenario, the MOSFET Q1 ormore generally switch device 220 of the sense circuit 124 limits thephase transition in the main current loop of the power circuit 110. Inthis scenario, di/dt increases responsive to increases in the draincurrent I_(D). Also, g_(fs)=f(I_(D)) is monotone rising also aspreviously described herein. The capacitor 210 of the sense circuit 124is charged by the conductive loop voltage ν_(antenna) for the duration tas given by:

$\begin{matrix}{v_{c} = {\left( {v_{antenna} - {2 \cdot v_{Fdiode}}} \right) \cdot \left( {1 - ^{- \frac{t}{\tau}}} \right)}} & (3)\end{matrix}$

where t is the transition time for a phase transition at the maincurrent loop of the power circuit 110 as shown in FIG. 3, ν_(Fdiode) isthe forward voltage of the diodes D1, D2, D3, D4, and τ is the timeconstant of the current sensing circuit 120. The time constant τ is aproduct of the resistive part of the conductive loop 122, diodes D1, D2,D3, D4 and capacitor 210, and the capacitance of the capacitor 210. Thetime constant τ is preferably chosen so that a significant voltagesignal can be obtained. In one embodiment, τ is chosen to be one thirdof the phase transition period PT_(period). For example, τ is 3.33 ns orless for a phase transition period of 10 ns. Continuing with this purelyillustrative example, the resistive components of the sense circuit 124may have a total resistance R of 1Ω. The capacitance of the capacitor210 in general is given by:

$\begin{matrix}{C = \frac{\tau}{R}} & (4)\end{matrix}$

with C=3.3 nF for this illustrative example.

The analysis circuit 126 senses the voltage V_(c) of the capacitor 210after a phase node transition as indicated by the Read event shown inFIG. 3. The analysis circuit 126 uses the sensed voltage to generate thecurrent information signal provided to the controller 130 as previouslydescribed herein. In addition, the analysis circuit 126 causes thecapacitor 210 to be reset by activating the Reset signal also shown inFIG. 3. The controller 130 manages one or more current dependentoperations of the power circuit 110 in response to the informationgenerated by the current sensing circuit 120.

FIG. 4 illustrates a top-down plan view of a portion of the power andcurrent sensing circuits 110, 120 e.g. as integrated together in thesame semiconductor die or on the same printed circuit board or package.According to this embodiment, the power circuit 110 includes at leastone power MOSFET 400 which forms part of the main current loop of thepower circuit 110. The conductive loop 122 of the current sensingcircuit 120 is spaced apart from and positioned over at least a portionof the power MOSFET 400. An electromagnetic field generated by the powerMOSFET 400 induces a voltage in the conductive loop 122 which isintegrated and stored by the capacitor 210 of the sense circuit 124 aspreviously described herein. The capacitor voltage is sensed andinterpreted by the analysis circuit 126 which generates one or morelogic signals which describe the current in the main current loop of thepower circuit 110, the logic signal(s) being input to the controller 130which is not shown in FIG. 3.

FIG. 5 illustrates an embodiment of an integrated circuit package 500that includes the power circuit 110 and the conductive loop 122 of thecurrent sensing circuit 120. The power circuit 110 includes a pluralityof transistors 502, 504 which form part of the main current loop of thepower circuit 110. The transistors 502, 504 are arranged in one or morelayers of the integrated circuit package 500. The conductive loop 122 ofthe current sensing circuit 120 is electrically decoupled from andspaced apart from the transistors 502, 504, but in close enoughproximity to at least part of the main current loop of the power circuit110 so that the conductive loop 122 can generate a voltage proportionalto the electromagnetic field generated responsive to a change in currentin the main current loop. The conductive loop 122 is arranged within theintegrated circuit package 500 in a different layer of the package 500than the transistors 502, 504.

In one embodiment, the power circuit includes a first MOSFET 502 and asecond MOSFET 504. The conductive loop 122 of the current sensingcircuit 120 is disposed over the first and second MOSFETs 502, 504 andan insulator layer 506 is interposed between the conductive loop 122 andthe first and second MOSFETs 502, 504. The first MOSFET 502 is ahigh-side MOSFET of a power converter circuit such as a synchronous buckconverter and the second MOSFET 504 is a low-side MOSFET of the powerconverter circuit according to an embodiment. The MOSFETs 502, 504 maybe integrated on the same die within the package 500 or separate dies asshown in FIG. 5.

The integrated circuit package 500 also includes a voltage plane 508, areference plane 510 (such as ground) and terminals for providingexternal connections points to the different components included in thepackage 500. Certain portions of the package 500 are not shown in FIG. 5so that the internal components are readily visible. The voltage plane508 is coupled to the drain 512 of the high-side MOSFET 502. A firstgate input terminal 514 is coupled to the gate 516 of the high-sideMOSFET 502 and a second gate input terminal 518 is coupled to the gate520 of the low-side MOSFET 504 for controlling the respective switchingstates of the MOSFETs 502, 504. The source 522 of the high-side MOSFET502 is coupled to the drain 524 of the low-side MOSFET 504 via a voltageoutput terminal 526 of the package 500. The source 528 of the low-sideMOSFET 504 is coupled to the reference plane 510. External connectionterminals are provided to the voltage and reference planes 508, 510, andare out of view in FIG. 5. One external terminal 530 is coupled to afirst end of the conductive loop 122 and another external terminal 532is coupled to the other end of the conductive loop 122 to provideconnection points for the conductive loop 122 at an external surface 534of the integrated circuit package 500.

FIG. 6 illustrates another embodiment of an integrated circuit package600 that includes the power circuit 110 and the conductive loop 122 ofthe current sensing circuit 120. FIG. 6 is similar to FIG. 5, except theconductive loop 122 is attached to the external surface 534 of theintegrated circuit package 600 instead of being embedded within thepackage 500 as shown in FIG. 5. The conductive loop 122 preferably isattached to the external surface 534 of the integrated circuit package600 positioned closest to the voltage output terminal 526 of the powercircuit 110. This way, the conductive loop 122 is closely coupled in theelectromagnetic sense to the power circuit 110 and the magnitude of thevoltage induced in the conductive loop 122 is sufficiently large.Depending on various considerations, one or more other components of thecurrent sensing circuit 120 can be embedded within and/or attached tothe packages 500, 600 shown in FIGS. 5 and 6. Otherwise, the externalconnection terminals 530, 532 coupled to the ends of the conductive loop122 provide adequate coupling to the other current sensing circuitcomponents.

Spatially relative terms such as “under”, “below”, “lower”, “over”,“upper” and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first”, “second”, and the like, are also used to describevarious elements, regions, sections, etc. and are also not intended tobe limiting. Like terms refer to like elements throughout thedescription.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

With the above range of variations and applications in mind, it shouldbe understood that the present invention is not limited by the foregoingdescription, nor is it limited by the accompanying drawings. Instead,the present invention is limited only by the following claims and theirlegal equivalents.

What is claimed is:
 1. An integrated circuit package, comprising: apower circuit including a plurality of transistors which form part of amain current loop of the power circuit, the plurality of transistorsarranged in one or more layers of the integrated circuit package; and aconductive loop electrically decoupled from the plurality oftransistors, the conductive loop being spaced apart from the pluralityof transistors and in close enough proximity to at least part of themain current loop so that the conductive loop is operable to generate avoltage proportional to an electromagnetic field generated responsive toa change in current in the main current loop.
 2. The integrated circuitpackage of claim 1, wherein the conductive loop is arranged within theintegrated circuit package in a different layer of the integratedcircuit package than the plurality of transistors.
 3. The integratedcircuit package of claim 1, wherein the conductive loop is attached toan external surface of the integrated circuit package.
 4. The integratedcircuit package of claim 1, further comprising a first external terminalcoupled to one end of the conductive loop and a second external terminalcoupled to the other end of the conductive loop, the first and secondexternal terminals providing connection points for the conductive loopat an external surface of the integrated circuit package.
 5. Theintegrated circuit package of claim 1, wherein the power circuitincludes a first MOSFET and a second MOSFET, the conductive loop ispositioned over at least a portion of the first MOSFET and at least aportion of the second MOSFET, and an insulator layer is interposedbetween the conductive loop and the first and second MOSFETs.
 6. Theintegrated circuit package of claim 5, wherein the first MOSFET is ahigh-side MOSFET of a power converter circuit and the second MOSFET is alow-side MOSFET of the power converter circuit.
 7. A method offabricating an integrated circuit package, comprising: arranging a powercircuit including a plurality of transistors which form part of a maincurrent loop of the power circuit in one or more layers of theintegrated circuit package; and arranging a conductive loop electricallydecoupled from and spaced apart from the plurality of transistors, theconductive loop being arranged in close enough proximity to at leastpart of the main current loop so that the conductive loop is operable togenerate a voltage proportional to an electromagnetic field generatedresponsive to a change in current in the main current loop.
 8. Themethod of claim 7, further comprising coupling a first external terminalto one end of the conductive loop and a second external terminal to theother end of the conductive loop so that the first and second externalterminals provide connection points for the conductive loop at anexternal surface of the integrated circuit package.
 9. The method ofclaim 7, further comprising: arranging the conductive loop over firstand second MOSFETs of the power circuit; and interposing an insulatorlayer between the conductive loop and the first and second MOSFETs. 10.The method of claim 9, further comprising positioning the conductiveloop over at least a portion of the first MOSFET and at least a portionof the second MOSFET.